FIG. 2 shows a prior art satellite communication system that allows the distribution of data from a data storage means provided in a base or ground station 101 via a satellite communication connection to an end-user community 103. The ground station 101 comprises a data storage means 110, e.g. a music or movie carrousel, as a data memory. A data manager 112 handles the requests sent from the respective user terminals 130 and ensures that the correct data are sent to the user terminal 130. A modulator means 114 is also part of the ground station 101. The modulator means 114 receives the data from the data storage means 110, modulates the data into a suitable data transmission format that is usually encrypted and sends these modulated data via a ground based satellite antenna 116 in an uplink data stream U′ to a satellite 102.
The uplink data stream U′ is received by a receiver 121 on-board of the satellite 102 through a first antenna 120 of the satellite 102 and is sent to a repeater means 122 on-board of the satellite 102. The repeater means 122 usually amplifies the received signals and sends them to a transmitter 123 connected to a second antenna 124 of the satellite 102 which transmits the amplified data as a downlink data stream D′ to a plurality of user terminals 130. The addressed user terminal 130 usually decrypts the received data stream and processes the obtained signals in order to provide the user with the appropriate entertainment, e.g. a movie displayed on a video screen.
This known satellite communication system requires that the uplink data stream U′ has the same data transmission rate as the downlink data stream D′. Consequently, the bandwidth for the uplink data stream U′ must be the same as for the downlink data stream D′.
This known technology wastes communication bandwidth of the uplink path and prolongs the access time at least by the uplink signal travelling time. A video-on-demand application for about 200 HDTV movie channels would require a data transmission rate of 580 Mbps of uplink rate and downlink rate, respectively.
U.S. Pat. No. 6,697,850 B1 discloses a satellite-based communications system having an on-board internet web proxy cache. A request for a selected web page is transmitted from either a standard terminal or an enhanced terminal to the satellite. The satellite initially determines whether the transmission came from a standard user or an enhanced terminal. If the request was from a standard terminal, the satellite relays the request for the web page directly to the ground station, which retrieves the requested web page from a local cache or the internet, and transmits the requested web page to the satellite, where the satellite in turn retransmits it to the user terminal. If the original request was transmitted from an enhanced terminal, then the satellite determines whether or not it already has a copy of the requested web page in its on-board memory cache. If the satellite has a copy in its memory cache, the requested web page is retrieved from its memory cache and transmitted to the enhanced terminal. If the satellite does not have a copy of the requested web page, it requests the page from the ground station. This known system is directed to the internet where the satellite is provided only with a cache memory in which already transmitted pages are cached. As these cached pages do not cover all possible user requests, the uplink data connection must have the same data transmission rate as the downlink data connection, so that also non-cached pages can be quickly transmitted to the user.